EFFECT OF RADIATIONS ON PHAGE PARTICLES 



79 



TABLE VI {Continued) 



" Inactivation dose = dose required to reduce titer of phage population to 

 the fraction \/e. 



radiating dilute phage suspensions in buffer, though some fraction 

 of the population must also be inactivated by the direct effect 

 under these conditions. The long-lived peroxides, in contrast, 

 may continue to cause damage long after the irradiation has 

 ceased. Watson (1952) called this second kind of indirect action 

 after effect. The properties of phage particles damaged by after 

 effect can be studied by diluting phages into medium previously 

 heavily X-irradiated and allowing the after effect to occur in the 

 absence of any direct irradiation of the particles themselves. 

 The results of such studies are summarized in Table V, where the 

 physiological properties of phages inactivated by ultraviolet light 

 and by direct, indirect, and after effects of X-rays are presented. 

 It is evident from this summary that the damage caused by in- 



